Certain types of magnetic separators use a structure of ferromagnetic material capable of retaining magnetic particles when magnetized and releasing them when de-magnetized. Such separators are used to separate the more magnetic components from a mixture of finely divided more and less magnetic particles carried by a stream of liquid (generally referred to as wet separations) or gas (generally referred to as dry separations) through the structure in question. Depending on factors such as the particle sizes involved, the structure in question may be a stack of grooved iron plates or a matrix of finely divided ferromagnetic filamentary material such as steel wool, wire mesh, or expanded metal. When the magnetic components to be removed constitute only a small fraction of the feed material, such as in the purification of kaolin for example, or in removing particulates from waste water, the matrix of magnetic material can be contained in a stationary canister and operated cyclically. The matrix is magnetized to collect magnetic particles until it is loaded to saturation, whereupon the magnetic field is turned off and the matrix is purged by a stream of liquid or gas. However, when the magnetic components to be removed constitute a major fraction of the feed material, as in the beneficiation of iron ores for example, the matrix becomes saturated too quickly to make cyclic operation practical. For such applications it is preferable to advance the matrix continuously through successive processing stations. The feed mixture, carried by liquid or gas, is introduced continuously in a region of magnetic field in a feed station, where the less magnetic particles pass through the matrix structure and exit through a discharge aperture, while the more magnetic particles are retained in the matrix structure and are carried out of the region of magnetic field, to be flushed or blown out in a region of zero (or near zero) magnetic field at a flush station. In addition, a rinsing stream is often used in a rinse station in a region of magnetic field in order to remove less magnetic particles which have become mechanically trapped in the matrix.
In such devices, the matrix is customarily carried in compartments or boxes, open at each end to provide for the inlet of the feed material at one end (the inlet end) and to provide for an outlet at the opposite end; these compartments may be part of a rigid cylinder or annulus, or they may be linked together to form an endless chain. In the prior art feed, slurry, and washing fluid is usually introduced in the open, that is by a nozzle or flow tube. Flexible gaskets or lips are sometimes used to confine the flow, but these are only spray deflectors rather than positive seals. The abrasive nature of granular slurries makes close tolerances difficult to maintain; and rubber gaskets or lips, particularly those in the transverse direction, tend to be too flexible to withstand any significant pressure differential.
Nevertheless, it is very important in several applications to maintain a positive seal between the matrix compartments and the outside, as well as between adjacent matrix compartments. There are several reasons for this requirement.
It is often desirable in wet separations to keep the matrix continuously submerged or flooded in order to maintain uniform slurry distribution and velocity, and to control the value of this flow velocity. Without seals the feed material, moving under the influence of gravity, might flow at an inconveniently high or inconveniently low rate. With seals the feed material can be made to flow at a predetermined optimized rate; and can even be made to flow vertically upward (relative to the direction of the gravity force). In particular, back flushing of the matrix, in a direction opposite to that in which it was fed, is possible with the aid of seals. Frequently it is advantageous to perform intermediate rinsing operations at higher pressure and velocity in order to remove intermediately magnetic particles or middlings, while the matrix is still in the magnetic field region, or to remove or flush mechanically trapped highly magnetic particles when the matrix is out of the magnetic field region. A positive seal is particularly important when handling materials which are either too valuable or too toxic to be permitted to leak out of the machine. In the case of dry separations the dusk leaking from a magnetic separator can represent an explosion hazard and/or a health hazard if inhaled. Seals also facilitate handling of viscous slurries.
Generally, seals allow operation at higher or lower pressure relative to atmospheric pressure. Air entrainment is often undesirable in wet separations and seals allow air entrainment to be reduced or eliminated.